1. Field of Invention
The present invention relates generally to an apparatus for facilitating the formation of cavities in bone or tissue structures for therapeutic applications. More particularly, the present invention relates to cannulae which may be utilized to penetrate bone or other tissue for applications involving the injection of or the implantation of material into the bone or other tissue.
2. Description of the Related Art
In vertebroplasty, cancellous bone of the vertebrae is supplemented with bone “cement,” e.g., polymethylmethacrylate (PMMA) or another filler material, in order to provide for anterior and posterior stabilization of the spine in various disease. As will be appreciated by those skilled in the art, a vertebra included in the spine includes an exterior formed from cortical bone, and an interior formed of cancellous or trabecular bone. Vertebroplasty often involves inserting a cannula into a target area of bone or tissue to achieve access to an implantation site for the bone cement.
Percutaneous vertebroplasty is desirable from the standpoint that it is minimally invasive as compared to a conventional alternative of surgically exposing a tissue site to be supplemented with bone cement. Several procedures are known for accessing a desired site in the cancellous bone of a vertebral body, or substantially any other cancellous bone, to deliver bone cement or any other suitable hard tissue implant material to stabilize, or build up, a site once expanded as taught by U.S. Pat. Nos. 6,280,456, 6,248,110, 5,108,404, and 4,969,888, which are each incorporated herein by reference.
To gain access to a hard tissue implantation site, as described in U.S. Pat. Nos. 6,019,776 and 6,933,411, which are each incorporated herein by reference, a straight needle or cannula in combination with a stylet may be employed. Once access is achieved and the stylet is removed from the cannula, bone cement may be delivered through the cannula for the purposes of filling the hard tissue implantation site. However, a shortcoming with the above mentioned straight cannula assembly is that once the cannula is driven into the bone body, there is no feature and/or structure to grip the bone wall and provide controlled advancement of the cannula.
Another cannula is shown in U.S. Pat. No. 6,679,886. Referring to FIG. 1, the prior art cannula includes threads at a distal portion. However, a shortcoming with the above mentioned threaded cannulae is that once the cannula is driven into the bone body, the threads are shaped such that the bone tends to be sheared as the cannula is inserted, destroying or stripping the bone wall. Consequently, controllably advancing the cannula is inhibited.
What is desirable is a cannula having a thread structure that facilitates convenient insertion, minimizes the damage to the bony wall, and maximizes the ability to be driven forward by the threads in a controlled manner.